Language sending lead mail depends on user language rather then parnter/reseller language

[ronaldotto]

Module

CRM

Describe the bug

When you have parnters/resellers (going to call them partners) and you get a lead or opportunity, you can assign that lead to a partner and send them an e-mail. That mail should be in the language of the selected partner but it is in the language of the user that sends it.

To Reproduce

Affected versions: 19

1. Have at least two languages installed an active
2. Create a company and make them a partner
3. Choose an other language than you have as a user
4. Create a lead
5. Go to the tab Assigned partner
6. Choose the created partner and send a mail. You will see it is in the user language.
7. Switch the user language and now it is in another language

Expected behavior
Mails should be created in the language selected in the card of the partner

Additional context
Version 19.0 on odoo.com
The send mail button.